FLT3 regulates β-catenin tyrosine phosphorylation, nuclear localization, and transcriptional activity in acute myeloid leukemia cells

Deregulated accumulation of nuclear β-catenin enhances transcription of β-catenin target genes and promotes malignant transformation. Recently, acute myeloid leukemia (AML) cells with activating mutations of FMS-like tyrosine kinase-3 (FLT3) were reported to display elevated β-catenin-dependent nuclear signaling. Tyrosine phosphorylation of β-catenin has been shown to promote its nuclear localization. Here, we examined the causal relationship between FLT3 activity and β-catenin nuclear localization. Compared to cells with wild-type FLT3 (FLT3-WT), cells with the FLT3 internal tandem duplication (FLT3-ITD) and tyrosine kinase domain mutation (FLT3-TKD) had elevated levels of tyrosine-phosphorylated β-catenin. Although β-catenin was localized mainly in the cytoplasm in FLT3-WT cells, it was primarily nuclear in FLT3-ITD cells. Treatment with FLT3 kinase inhibitors or FLT3 silencing with RNAi decreased β-catenin tyrosine phosphorylation and nuclear localization. Conversely, treatment of FLT3-WT cells with FLT3 ligand increased tyrosine phosphorylation and nuclear accumulation of β-catenin. Endogenous β-catenin co-immunoprecipitated with endogenous activated FLT3, and recombinant activated FLT3 directly phosphorylated recombinant β-catenin. Finally, FLT3 inhibitor decreased tyrosine phosphorylation of β-catenin in leukemia cells obtained from FLT3-ITD-positive AML patients. These data demonstrate that FLT3 activation induces β-catenin tyrosine phosphorylation and nuclear localization, and thus suggest a mechanism for the association of FLT3 activation and β-catenin oncogeneic signaling in AML.